1. Field of the Invention
The present invention relates generally to roofing seals, and more particularly to an improved shield device for forming a permanent weather-tight seal to a vent pipe and over a roof flashing.
2. Brief Description of the Prior Art
A number of specialized devices have been developed over the years to form a seal between a roof and a pipe projecting through that roof. These include roof flashing devices having a flat plate with a centralized, upwardly projecting, tapered housing with an opening. The flat plate is attached to the roof, and the vent pipe passes through the opening in the tapered housing. The housing and the pipe are often sealed with a caulking or other mastic-like material.
The prior art teaches several roof flashing structures which use a sealing ring to attempt to create a more permanent, weather-proof seal. For example, Gustafson (U.S. Pat. No. 3,677,576) and Logsdon (U.S. Pat. Nos. 4,010,578 and 4,160,347) disclose roof flashing structures which integrally include an elastomeric sealing member for forming a better seal between the vent pipe and the roof. Willoughby (U.S. Pat. No. 4,512,119) teaches another way to seal a roof flashing to a pipe, with an annular rubber washer and a neoprene weather apron.
Independent seals, which are not integrally included with a roof flashing structure, are also known in the prior art. The prior art independent seal products are not part of a flashing structure which provides support. Therefore, they have used relatively rigid plastic material. Such devices are forced down over the vent pipes. A series of annular sealing rings on the inner surface of the seal device engage the vent pipe to form a series of seals.
Roof flashing sealing devices are subject to considerable stress. When the ambient temperature rises and falls, both a building and a vent pipe extending through a roof will expand and contract. These expansions and contractions with varying temperature do not occur at the same rate. Thus, the building roof and the vent pipe will move upward or downward by different amounts with a given temperature variance. The device used to seal a vent pipe to a roof flashing is subject to these movements.
The prior art roof flashing devices with elastomeric seals have several disadvantages related to these movements. The upward and downward cycling of the sealing device reduces the effectiveness of the seal. Roof flashing devices which include an integral elastomeric sealing member can invert under certain conditions. Once inversion occurs, water can accumulate in the inverted seal, and the combination of sunlight on the inverted seal and water sitting in the seal cause the sealing member to decompose. Roof flashing devices with an integral sealing member also are significantly more expensive than independent seal products.
The prior art independent seals also have a number of disadvantages. These problems begin at the time the seals are applied. Since they are composed of relatively rigid plastic, they must be hammered onto the vent pipe. Thus, their application could lead to cracking and crazing. The use of relatively rigid plastic also prevents the seal from conforming to the vent pipe; the hard material will bridge any discontinuity in the pipe.
As with the combination roof flashing/elastomeric seal devices, the effectiveness of independent sealing devices is also reduced by the upward and downward cycling of the sealing device with temperature variation. The relatively rigid seals of the prior art do not slide up and down with thermal expansion and contraction. Instead, the rigid seal becomes distorted and does not conform to the vent pipe that it surrounds. Prior art independent seals which use a series of relatively narrow seals may quickly lose their effectiveness with thermal cycling. Moreover, the rigid independent seals of the prior art are susceptible to cold-flow and creep, which makes the distortion problem worse. This failure to conform to the vent pipe causes stress in the seal, leading to faster aging of the seal.
Neither the integral roof flashing/elastomeric seal nor the relatively rigid independent seal tolerates contamination on a vent pipe (such as paint, cement, or glue) very well. In addition, neither works well when a roof has two vent pipes close together. In the past, these situations have generally been handled with a "pitch pan", where a pan is filled with a filler such as mastic, foam, or concrete, and covered with asphalt or another sealer.